Properties of Al_xGa_1-xAs grown from a mixed Ga-Bi melt

Thick smoothly graded Al_xGa_1-xAs layers (50-100 µm) are used in light-emitting diode structures and also for creation of high-power photovoltaic converters with side-input of laser radiation. To achieve the required thickness of the Al_xGa_1-xAs layer the high temperature LPE growth technique is required. However high epitaxial temperature increases the unintentional doping level. Epitaxy from mixed Ga-Bi melts was investigated as a way to solve this problem. It was found that for growing relatively thick Al_xGa_1-xAs layers, it is expedient to use Ga-Bi melts with 20 at% or less bismuth content. SIMS and Hall characterization of Al_xGa_1-xAs layers revealed that the growth of Al_xGa_1-xAs from mixed Ga-Bi melts reduces the background doping level (including carbon) and influences the native defect formation keeping the n-type conductivity. This effect is explained by the changes of the group III and V elements concentrations in the melt as well as Bi incorporation in the lattice.